CentOS SSH Installation And Configuration

How do I install and configure ssh server and client under CentOS Linux operating systems? Can you explains CentOS SSH installation commands?

OpenSSH is a free and open source software for remote login and running commands on CentOS enterprise Linux server or desktop systems. In this tutorial, we will learn how to install ssh server/client and configure the same.

CentOS SSH Installation

You need to install the following packages (which are installed by default until and unless you removed it or skipped it while installing CentOS):

• openssh-clients : The OpenSSH client applications
• openssh-server : The OpenSSH server daemon

Let us see all steps in details.

OpenSSH Installations under CentOS Linux

To install the server and client type the following command as root user:
# yum -y install openssh-server openssh-clients

CentOS 6.x and older commands

Start the service:
# chkconfig sshd on
# service sshd start
Make sure port 22 is opened:
# netstat -tulpn | grep :22

Firewall Settings For CentOS 6.x and older

Edit /etc/sysconfig/iptables (IPv4 firewall),
# vi /etc/sysconfig/iptables
Add the lines:

Replace RH-Firewall-1-INPUT with actual chains in your config file. See CentOS/Redhat (RHEL 6.x) tutorial page for more info.

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
If you want to restict access to 192.168.1.0/24, edit it as follows:
-A RH-Firewall-1-INPUT -s 192.168.1.0/24 -m state --state NEW -p tcp --dport 22 -j ACCEPT
If your site uses IPv6, and you are editing ip6tables, use the line:
-A RH-Firewall-1-INPUT -m tcp -p tcp --dport 22 -j ACCEPT
Save and close the file. Restart iptables:
# service iptables restart

CentOS 7.x/8.x and above commands

Enable and start the sshd service:
# systemctl enable sshd.service
# systemctl start sshd.service
Verify that TCP port number 22 is in listing state using the ss command/netstat command along with the grep command:
ss -tulpn | grep ':22'
OR
ss -tulpn | grep ':22'
Open tcp port 22 using the firewall-cmd command # firewall-cmd --zone=public --add-service=ssh --permanent
# firewall-cmd --reload

OpenSSH Server Configuration

Edit /etc/ssh/sshd_config, enter:
# vi /etc/ssh/sshd_config
To disable root logins, edit or add as follows:
PermitRootLogin no
Restrict login to user tom and jerry only over ssh:
AllowUsers tom jerry
Change ssh port i.e. run it on a non-standard port like 1235
Port 1235
Save and close the file. Restart sshd:
# service sshd restart ## centos 6.x ##
OR
# systemctl restart sshd.service ## centos 7.x/8.x ##

How to test ssh installation

Use the ssh command/scp command or sftp command as follows:
ssh user@your-server-ip
ssh vivek@server1.cyberciti.biz
ssh vivek@server1.cyberciti.biz uptime
sftp server1.cyberciti.biz
scp foo.gif vivek@ln.cbz01:/home/httpd/images

Conclusion

You learned how to install openssh server (sshd) and clients on CentOS Linux using the yum command. For more information please see the following tutorial:

• Top 20 OpenSSH Server Best Security Practices

Category	List of Unix and Linux commands
File Management	cat
Firewall	Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04
Network Utilities	dig • host • ip • nmap
OpenVPN	CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04
Package Manager	apk • apt
Processes Management	bg • chroot • cron • disown • fg • jobs • killall • kill • pidof • pstree • pwdx • time
Searching	grep • whereis • which
User Information	groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w
WireGuard VPN	Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04